Physical inactivity occurs among 65% to 95% of youth with type 1 diabetes (T1D) and based upon limited evidence may contribute to the rapidly growing incidence of overweight among this population. The purpose of the present study is to pilot test a 12-week intensive lifestyle program for adolescents with overweight and T1D utilizing group exercise classes adapted for this population, supplemented with coping skills training and diabetes self-management education to address problem solving behaviors that limit their physical activity and weight control. Our primary aim is to evaluate the changes in physical activity adherence, anthropometrics, and self-management behaviors following this program among sedentary adolescents with T1D and overweight (n=25, OW) compared with sedentary adolescents with T1D and normal weight (n=25, NW). We hypothesize that the OW group will achieve improve physical activity adherence and anthropometrics to the same or greater extent as the NW group and previous Bright Bodies cohorts, and that these changes will correlate with improved exercise-related problem solving. Our secondary aim is to evaluate changes in adipocytokines and epigenetic factors related to the etiology of overweight/obesity following our physical activity intervention. We hypothesize changes in these biomarkers will correlate with changes in anthropometry variables and partially explain any differences in response between the groups and individuals should those occur.